1. Field of the Invention
The present invention relates to compositions which assist in the corrosion protection of magnesium, magnesium-aluminum, aluminum-magnesium and aluminum alloys in engine coolants and heat-exchange fluids. Aliphatic mono- or di-basic acids or aromatic carboxylate acids, or the alkali metal, ammonium or amine salts thereof, have been found to provide corrosion protection to magnesium, in addition to the protection that these acids already provide to other metals, such as aluminum, iron, copper and solder, when combined with a fluoride or a fluorocarboxylic acid or a salt thereof. Specific combinations of such acids or salts with fluoro compounds have been found to provide synergistic corrosion protection for magnesium. The optional addition of a hydrocarbyl triazole and/or a thiazole to these combinations provides improved corrosion protection, particularly to copper alloys but also to other metals such as aluminum. The presence of the fluoride and/or a fluorocarboxylate has been found to significantly improve the high temperature magnesium corrosion protection properties for individual carboxylates, for combinations of carboxylates, and for combinations of carboxylates and hydrocarbyl triazoles and/or thiazoles.
Automobile engine cooling systems contain a variety of metals, including copper, solder, brass, steel, cast iron, aluminum, magnesium, and their alloys. The possibility of corrosive attack on such metals is high, due to the presence of various ions as well as the high temperatures, pressures, and flow rates found in such cooling systems. The presence of corrosion products within the cooling system can interfere with heat transfer from the engine combustion chambers, which may subsequently cause engine overheating and engine component failure due to excess metal temperatures. See generally Fay, xe2x80x9cAntifreezes and Deicing Fluids,xe2x80x9d Kirk-Othmer Encyclopaedia of Chemical Technology (1978) ed, vol 3, pp 79-95. It would therefore be generally advantageous if the formation of corrosion products within automobile cooling systems could be controlled or eliminated. It is one object of the instant invention to provide a corrosion inhibitor useful in the prevention and control of corrosion in automobile engine cooling systems containing various metals, particularly magnesium.
The trend towards improved fuel economy for automobiles has led to the increased use of lightweight materials such as aluminum and magnesium alloys for engine and cooling system components. However, it has been found that pitting and crevice corrosion are particularly prevalent in aluminum and magnesium-containing cooling systems. Pitting of thin-walled automobile radiator tubes may lead to tube perforation. Crevice corrosion at cylinder head packings or coolant hose connections may also occur. Both types of corrosion may lead to eventual coolant loss, with subsequent engine overheating and component failure. Other forms of localized corrosion such as deposit attack from deposition of corrosion products may also result.
Many conventional corrosion inhibitor additives used in automobile cooling systems do not provide adequate protection against the pitting, crevice, and deposit attack corrosion phenomena found with magnesium, aluminum and various other metal alloys. It would therefore be particularly advantageous if such localized corrosion phenomena could be controlled or eliminated. It is another object of the instant invention to provide a corrosion inhibitor for use in automobile cooling systems, which prevents or controls localized corrosion of magnesium.
All corrosion inhibitors employed in automobile antifreeze/coolant formulations are gradually depleted by use and the build-up of corrosion products in the cooling system. It would thus be advantageous if the build-up of corrosion products within the system and subsequent corrosion inhibitor depletion or degradation could be controlled or eliminated. It is a further object of the instant invention to provide a corrosion inhibitor which is less prone to depletion or degradation than traditional corrosion inhibitors used in antifreeze/coolant formulations.
Organic Acid Technology (OAT) coolants and heat exchange fluids have been introduced, providing improved corrosion protection and having a long life. OAT corrosion-inhibitor packages in aqueous and glycol concentrates are used in automotive, heavy duty, marine and industrial applications. OAT corrosion-inhibitors are also used in secondary cooling systems and in a variety of industrial heat exchange fluids. Several U.S. and foreign patent references disclose the use of carboxylic acids, or the salts of such acids as corrosion inhibitors in antifreeze/coolant and heat-exchange fluid compositions. These compositions are optimized for the protection of aluminum and other materials currently used in the above applications.
Various corrosion inhibitors have been added to heat transfer fluids to reduce corrosion of metallic systems. For example, U.S. Pat. No. 4,587,028 (Darden) discloses non-silicate antifreeze formulations containing alkali metal salts of benzoic acid, dicarboxylic acid and nitrate. Additional ingredients including alkali metal hydroxides, alkali metal nitrates and aromatic triazoles, such as tolyltriazole or benzotriazole are preferably provided. U.S. Pat. No. 4,647,392 (Darden et al) discloses corrosion inhibitors using aliphatic monobasic acids or salts, hydrocarbyl dibasic acids or salts and hydrocarbonyl triazole. U.S. Pat. No. 4,657,689 (Darden) discloses corrosion inhibitors containing aliphatic monobasic acids or salts, hydrocarbyl dibasic acids or salts, hydrocarbyl azoles and specific hydrocarbyl alkali metal sulfonates. U.S. Pat. No. 5,085,791 (Burns) discloses antifreeze compositions containing cyclohexane acid corrosion inhibitor alone or in combination with other corrosion inhibitors, particularly sebacic acid and tolyltriazole. The cyclohexane acid includes cyclohexyl carboxylic (formic) acid, cyclohexyl acetic acid and cyclohexyl propionic acid. The cyclohexane acid is targeted to inhibit lead solder and/or aluminum corrosion. U.S. Pat. No. 4,105,405 (Wehle et al) discloses the use of cyclohexane hexacarboxylic acid corrosion inhibitors.
JP-A-08 020763 (Seiken Kogaku Kogyo KK) describes a fluid for use as a coolant in internal combustion engines comprising glycol, water, a magnesium compound, an alkyl benzoic acid (e.g. p-tert-butylbenzoic acid) or a salt, a do-decane diacid or a salt and a triazole or thiazole.
JP-A-08 085782 (Nippon Chem Kogyo KK) describes a glycol based antifreeze composition containing a dodecanedioic acid or a salt, p-tert-butylbenzoic acid or a salt and a triazole, together with a silicate, molybdate, benzoate or thiazole. The composition is free from amines, phosphates, borates and nitrites.
Engine manufacturers are now evaluating the use of magnesium as a material for engine and heat-transfer systems. Traditional inhibitor packages do not give adequate corrosion protection to magnesium components. In general, currently used OAT coolants are only mildly aggressive, but the protection levels for magnesium are not sufficient, particularly at the high temperatures found in working engines. Previous research has indicated that a combination of an alkylbenzoic acid (4-tert-butylbenzoic acid), an aliphatic monoacid (octanoic acid) and a hydrocarbyl triazole (tolyltriazole), provides improved corrosion protection for magnesium, in comparison with traditional and OAT coolant formulations (Table 1 in U.S. Pat. No. 4,851,145 (van Neste)). EP-A-0229254 (Asahi Glass Co Ltd) describes an electrolytic capacitor comprising a capacitor element and an electrolyte impregnated into the element, wherein the electrolyte contains a fluorocarboxylic acid or salt dissolved in an organic solvent.
There is need for a coolant system which provides high levels of corrosion protection to magnesium components.
The present invention relates to an antifreeze concentrate composition comprising one or more inhibitors selected from alkylbenzoic acid, C5-C15 mono- or di-basic acid or salts thereof, together with a fluoride and/or a fluorocarboxylic acid or salt thereof.
Amongst the aromatic carboxylates, the group of alkylbenzoic acids of general formula:
Rxe2x80x94Arxe2x80x94COOH 
where Ar is benzyl and R is a C1-C8 alkyl radical or an element of group 7, e.g. F, are preferred. 4-Tert-butylbenzoic acid (hereafter referred to as PTBBA), is the most preferred alkylbenzoic acid and 4-fluoro benzoic acid is the most preferred compound when R is an element of group 7. Alkali metal, ammonium or amine salts of the alkylbenzoic acid may be used. The most preferred alkali metal salts are potassium and sodium.
Aliphatic carboxylate acids that provide corrosion protection may be any C5-C15 aliphatic monobasic acid or dibasic acid or the alkali metal, ammonium or amine salt of said acids. Heptanoic acid, octanoic acid, and nonanoic acid (or isomers thereof), and mixtures thereof are the preferred monobasic acids. Decanoic acid and undecanoic acid provide good protection but solubility of the higher alkyl acids in water is limited. Of the dibasic acids, dodecanedioic acid provides reasonably good magnesium protection. Of the naphtylcarboxylic acids, 1-naphtylcarboxylic acid is the preferred carboxylic acid.
It has been found that the combination of one or more of the above described acids, together with the fluoro compound, gives a synergetic effect for improved magnesium protection. The combination of PTBBA and octanoic acid is especially preferred. Nonanoic and heptanoic acid are good alternatives for octanoic acid. Compositions formulated with no hydrocarbyl triazole give good magnesium protection, or hydrocarbyl triazole at a level below 0.2 wt %. The addition of a hydrocarbyl triazole to these combinations provides additional copper protection, as expected. Improved corrosion protection properties were found for the other metals, especially for aluminum.
It has been found that the addition of a fluoride or a fluoro carboxylate to an aliphatic carboxylic acid or to an alkylbenzoic acid or to the preferred synergistic combinations of alkylbenzoic acids and the preferred monocarboxylic acids, significantly improves the high temperature corrosion protection properties of the formulation. Most particularly, such systems give improved protection against magnesium corrosion.
The present invention firstly identifies a group of specific aliphatic and aromatic carboxylates that provide improved corrosion protection, when used with a fluoride and/or a fluorocarboxylic acid or salt thereof.
Amongst the aromatic carboxylates are preferred the group of alkylbenzoic acids of general formula:
Rxe2x80x94Arxe2x80x94COOH 
where Ar is benzyl and R is a C1-C8 alkyl radical. In this invention, 4-tert-butylbenzoic acid (PTBBA) is preferred. Any alkali metal, ammonium or amine salts of the alkylbenzoic acid may be used to form the alkylbenzoic acid salt; however, alkali metals are preferred. The most preferred alkali metal salts are potassium and sodium. Of the naphtylcarboxylic acids, 1-naphtylcarboxylic acid is the preferred carboxylic acid.
Aliphatic carboxylate acids that provide corrosion protection may be any C5-C15 aliphatic monobasic acid or dibasic acid or the alkali metal, ammonium or amine salt of said acids. This would include one or more of the following acids or isomers thereof: heptanoic acid, octanoic acid, and nonanoic acid, and mixtures thereof are the preferred monobasic acids. Decanoic acid and undecanoic acid provide good protection but solubility of the higher alkyl acids in water is limited. Of the dibasic acids, dodecanedioic acid provides reasonably good magnesium protection.
Combinations of one or multiples of the above mentioned aromatic carboxylates with one or more aliphatic carboxylates, together with the fluoro compound, give a synergistic effect for the protection of magnesium alloys. When using a hydrocarbyl triazole component such as an aromatic triazole or an alkyl substituted aromatic triazole such as benzotriazole or tolyltriazole, increased protection of copper is achieved. Improved protection of other metals, particularly aluminum is also observed. For magnesium protection alone the use of a hydrocarbyl triazole is optional.
The additional inhibitor which now provides superior synergistic corrosion protection, especially for magnesium alloys, especially at elevated temperatures, in combination with one carboxylic acid or with a synergetic mixtures of multiple acids such as the combination of aliphatic carboxylates with the alkylbenzoic acids, such as mentioned above, is fluoride. Used alone, fluoride provides a very low level of protection. It is an important aspect of this invention that fluor compounds such as fluorides and/or fluoro carboxylates, in combination with aliphatic carboxylates or alkylbenzoic acids give a synergistic effect to significantly reduce corrosion, especially of magnesium at elevated temperatures. The fluoride can be introduced in the formulation as hydrogen fluoride and/or a fluoro carboxylic acid or the alkali metal, ammonium or amine soluble salt of the mentioned acid.
The combination of the corrosion inhibitors of the instant invention will most typically be employed in antifreeze formulations as a coolant for internal combustion engines. Other applications may include hydraulic fluids, aqueous cutting oils, paints, soluble oils, metal cutting fluids, aircraft deicers, and greases. In these applications the aliphatic acids and alkylbenzoates may be formed with metal hydroxides including sodium, potassium, lithium and barium.
In a preferred embodiment of the instant invention, the above described corrosion inhibitors may be employed in a mixture with a liquid alcohol freezing point depressant to form a novel antifreeze/coolant concentrate composition for use in the cooling systems of internal combustion engines. The coolant concentrate composition preferably comprises: from 80-99 weight percent of a water soluble liquid alcohol freezing point depressant; from 0.01-15, preferably 0.1-5 weight percent of the above described alkylbenzoic acid/salt and/or aliphatic carboxylic acid/salt component and from 0.005-5, preferably 0.01-1 weight percent of hydrogen fluoride and/or a fluoro carboxylate. In addition one of the above mentioned components, hydrocarbyl triazole components can optionally be used at from 0.005-1, preferably 0.1-0.3 weight percent.
The liquid alcohol freezing point depressant component of the above described coolant in the instant invention includes glycols such as ethylene glycol, di-ethylene glycol, propylene glycol, di-propylene glycol and glycol monoethers such as the methyl, ethyl, propyl and butyl ethers of ethylene glycol, di-ethylene glycol, propylene glycol and di-propylene glycol. Ethylene and propylene glycol are particularly preferred as the freezing point depressant component. In the above described coolant concentrate composition of the instant invention, an additional dicarboxylic acid preferably dodecanoic diacid, may be employed at concentrations of 0.01-15.0 weight percent, preferably 0.1-5.0 weight percent. Additional conventional corrosion inhibitors such as alkali metal borates, silicates, benzoates, nitrates, nitrites, molybdates or hydrocarbyl thiazoles may also be employed at concentrations of 0.01-5.0 weight percent.
In another embodiment of the invention, the above described corrosion inhibited coolant concentrate composition is diluted with 10-90 volume percent, preferably 25-75 volume percent of water. In yet another embodiment of the invention, the above described corrosion inhibitor combinations are used in aqueous solutions of alternative freezing point depressants such as organic acid salt solutions. Acetates, formates and proprionates are particularly preferred.